Motor pump units for circulation systems such as hot water heating have long used couplings to join the shaft of the motor unit to the pump unit for the transmission of torque to operate the pump. The pump unit is installed in the water line and has a housing which encloses a shaft upon which the pump itself is mounted in the housing. The motor unit in its housing has a shaft extending therefrom. The units are assembled by bolting together the opposing faces of the housings covering the respective extending stub shafts. When so assembled the space between the ends of the respective stub shafts is seldom greater than one-quarter inch. The coupling to join the two stub shafts for transmission of the motor to the pump must have a certain flexibility in it to protect the motor, and stops noise from transmitting through the piping in the system. The most important part of the coupling is the overall size that will fit into these small pump assemblies. The space between pump housing and motor housing is very critical.
A type of flexible coupling used for circulating pump units is disclosed in U.S. Pat. No. 3,280,242. Between 75 and 85 percent of circulating pump units used in hot water heating systems employ this coupling disclosed in this patent. Assembly of a motor pump unit employing the disclosed coupling is time consuming and requires a considerable amount of dexterity. In practice one of the hubs of the coupling is secured to one shaft, for example that of the pump. The motor unit is held in one hand at the approximate level of the pump unit and the other hub is then slid onto the motor shaft. The coupling must then be turned about the motor shaft unit so that the arms on that hub cause the flexible springs to at least be spread out. Then while holding the hub in this position with one hand, the same hand must attempt to tighten the set screw in the hub on the motor shaft to lock the hub in that position. After this has been accomplished, the two units may be bolted or otherwise secured together depending upon the design of the unit. Should one of the spring elements in this type of coupling break or pull out of its arm, then the entire unit must be disassembled and the coupling removed from both shafts. A replacement of the coupling follows the procedure outlined previously.